In recent years there has been considerable interest in determining the position of user devices, such as cellular telephones, portable electronic computers and other portable personal user devices. Systems based on the use of global satellite navigation systems (e.g. GPS) are useful out of doors but are of limited use within buildings and have only limited positioning accuracy. Accordingly, it is desirable to determine the position of user devices using alternative technologies, particularly those which are useful indoors, either as an alternative to or in combination with global satellite navigation systems to obtain more accurate measurements of position.
It is known to determine position by detecting radio beacons which transmit radio signals over relatively low distances, for example, connectable radio beacons which allows access to a LAN and non-connectable radio beacons which simply transmit data, such as their identifier. Using a database of the position of such radio beacons it is possible to determine position using techniques such as measuring received signal strength and triangulation.
The invention aims to provide improvements to these technologies, to enable more accurate measurements of position to be made, or to enable measurements to be made more simply, for example, some embodiments enable an estimate of position without a requirement to measure received signal strength. The invention also provides radio beacons which facilitate the methods of the invention.